1. Field of the Invention
The invention relates to an image forming apparatus, and particularly to jam clearance when a duplex unit is detachably mounted.
2. Related Background Art
Among image forming apparatuses such as printers and copying machines, there is one adapted to form a toner image by an electrophotographic recording method, and thereafter transfer the toner image to a sheet, and then apply heat and pressure to the sheet to thereby fix the toner image.
FIGS. 19A and 19B of the accompanying drawings show the construction of a laser printer which is an example of such a conventional image forming apparatus, and this laser printer 201 is comprised of known sheet feeding means, image forming means, a fixing device 250, etc. A duplex unit 300 for performing printing (image formation) on the two sides of a sheet is adapted to be detachably mounted on this laser printer 201.
In such a laser printer 201, the duplex unit 300 is adapted to be inserted from the rear (the left as viewed in FIG. 19A) into the interior of the printer and mounted, but when the duplex unit 300 is thus mounted, a portion of the duplex unit 300 protrudes from the exterior surface of the laser printer 201 to the outside (rear side) thereof. On this protrusion 300a, there are disposed, a control substrate 301 for controlling the duplex unit, a fan 302 for cooling the laser printer 201, and a driving portion necessary when two-side printing is performed.
Now, in such a laser printer 201, when the jam of a sheet S1 occurs in a fixing device 250 or downstream of the fixing device 250, the rear cover 210 of the laser printer 201 is adapted to be opened in a case where the duplex unit 300 is not mounted. There is a construction in which when the rear cover 210 is thus opened, the nipping of the sheet S1 by the heating roller 251 and pressure roller 252 is released by nip pressure releasing means (not shown) in operative association with the opening operation of the rear cover 210 so that the clearance of the jamming sheet S1 may become easy. Such a construction is disclosed in Japanese Patent Application Laid-open No. H06-186880. By the rear cover 210 being thus opened and also, the nipping of the sheet S1 by the heating roller 251 and the pressure roller 252 being released, a space permitting the access to the jamming sheet S1 is secured and also, the sheet S1 can be pulled out easily.
On the other hand, in a case where as shown in FIG. 19A, the duplex unit 300 is mounted, the protrusion 300 becomes a hindrance and the rear cover 210 cannot be opened and therefore, when jam clearance is to be done, the duplex unit 300 is first drawn out in the direction indicated by the arrow in FIG. 19A and moved to a jam clearance position, or the duplex unit 300 is intactly drawn out. Thereafter, as shown in FIG. 19B, the rear cover 210 is opened in the direction indicated by the arrow.
In such a conventional image forming apparatus, however, if the duplex unit 300 is not mounted, the number of steps necessary for jam clearance is only one, i.e., the opening of the rear cover 210, but if the duplex unit 300 is mounted, another step of drawing out the duplex unit 300 becomes necessary.
Not only when the sheet S1 stagnates in a duplex path during two-side printing, but also when the sheet S stagnates inside the rear cover 210 during one-side printing, it is necessary to slide the duplex unit 300 and move it to the jam clearance position at first, or to draw out the duplex unit, and thereafter open the rear cover 210. That is, when the duplex unit 300 has been mounted, there has arisen the problem that much time is required for jam clearance and usability (operability) is reduced.